1. Field of the Invention
The present invention generally relates to a coatable inorganic material and a method for fabricating a disc stamper using the same.
2. Description of Related Art
Along with the development of high definition televisions (HD-TV), some high density optical discs are demanded to have a capacity of up to 25 GB on a single layer at a single surface. The capacity on a single layer at a single surface may even reach up to 100 GB in the near future, which requires the size of recording spots to be minimized to less than 100 nm. Therefore, storage technologies in sub-terabyte level or terabyte level will become an important research topic of the manufacturers in the field.
As to the disc recording process, the property of the photoresist material used therein is one of the critical factors that affect the defining ability of a disc master pattern. In a conventional deep ultraviolet light (DUV) laser beam direct write mastering process, the photoresist generally used is an organic photoresist system. For a laser beam recorder system with a DUV wavelength of 257 nm, or 266 nm, the maximum NA of an adopted objective lens is 0.9, and the minimum spot size thereof is about 150 nm in theory. The above laser beam recorder systems employ two different kinds of photo mode organic photoresists generally used at present, which are I-line photoresist and chemical amplified type photoresist (DUV CA photoresist), respectively, and the contrast (γ) of this kind of photoresist and the obtainable minimum pattern size definition capability are mostly considered in selecting the photoresist.
Taking the current research data in general, it is known that the maximum contrast of the I-line photoresist is usually 3, the contrast of the DUV chemical amplified type photoresist is 8, and the optimal pattern resolution thereof can reach the minimum pattern structure size of 130 nm to 180 nm. That is to say, the current DUV laser beam recorder systems with the mentioned organic photoresists cannot meet the requirements of nano-scale pattern definition capability (≦100 nm). Additionally, in regard to I-line photoresist, besides having a contrast not high enough, this type of photoresist also has an insufficient transparency to DUV light, such that this photoresist cannot achieve a higher resolution capability. Although the other type of chemical amplified type photoresist has a higher contrast γ (about two times of that of the I-line photoresist), the polymer main chain of this type of photoresist is easily contaminated by environment, resulting in the limitation of the usage of this type of photoresist. Further, the I-line photoresist and the chemical amplified type photoresist are composed of a polymer with chain structure of high molecular weight. Thus, the surface roughness of the pattern after development becomes higher due to the molecular cluster property of the polymer.
As described above, for the current DUV laser of 257/266 nm and the laser beam recorder system with a high NA of 0.9, if the laser wavelength is further reduced or a near-field optical laser beam recorder system (NA>1) is developed, the mechanical precision and the control precision must be improved, and the component cost and production cost of the device will be greatly increased, thus limiting the development thereof. Therefore, in the nano-scale laser beam direct write mastering technique, it is a major issue to be solved urgently on how to overcome the optical diffraction limit of the laser beam recorder machine. The possibility of using a material process technique together with the existing laser beam recorder system as a solution can not only overcome the seemingly insuperable optical diffraction limit, but also effectively reduce the production cost of the device.
Recently, there is phase transition mastering (PTM) technology involving forming films by a sputtering process, used for fabricating a disc stamper, which process is illustrated in FIG. 1.
Referring to FIG. 1, in step 100, a substrate is provided, and then a phase change metal or oxide target material is sputtered on the substrate in the manner of sputtering film formation by a high-vacuum sputtering system (Step 102), and most of this type of inorganic resist material can complete the laser beam direct write mastering process by controlling the phase change between the crystalline and amorphous phase of the alloy thin film. The sputtering resist generally is a chalcogenide material or a metal oxide formed by sputtering, and in this figure a layer of chalcogenide material is taken as an example. Afterward, the layer of chalcogenide material is exposed by a laser (Step 104). Then, an additional specific wet etching solution is needed to reserve or remove the region generated through thermochemical reaction, i.e., to develop, so as to form a pattern (Step 106). Next, nickel is electroplated on the pattern to form a nickel layer (Step 108). Finally, the nickel layer and the pattern on the substrate are separated (Step 110).
However, the sputtering phase transition laser beam direct write mastering technique adopts a phase change metal resist film that is sputtered by a high-cost and complicated vacuum sputtering coating system, such that the device cost is much higher than that of the conventional photoresist spin coating film-formation process and the wet etching solution is special. Additionally, the reflectance of the film layer of phase change metal resist is too high, and cannot be used in a laser beam recorder with auto-focusing servo system. If the layer of phase change metal resist, utilized in the sputtered phase transition mastering (PTM), is adopted, it is needed to purchase an entirely new process device, thus resulting in a great increment in the investment of the device.